Practically thickness of mortar joint in masonry is restricted to an inch. if due to any reason the thickness gets increase, it is better to use 10mm aggregates in mortar.
Going above 1 inch thickness will cause a settlement and cracking issues in wall.
Ideal thickness of mortar joint in masonry would be around 10mm or up to 1/2 inch.
To make uniform vertical joints in brick masonry, a piece of old plywood shutters can be use which is 12 mm in thickness.